Fuel cell technology has been identified as a potential alternative for the traditional internal-combustion engine conventionally used to power automobiles. It has been found that fuel cell power plants are capable of achieving efficiencies as high as 55%, as compared to a maximum efficiency of about 30% for internal combustion engines. Furthermore, fuel cell power plants produce no hydrocarbon emissions.
Fuel cells, generally, include three components: a cathode, an anode and an electrolyte which is sandwiched between the cathode and the anode. Oxygen from the air is reduced at the cathode and is converted to negatively-charged oxygen ions. These ions travel through the electrolyte to the anode, where they react with a fuel such as hydrogen. The fuel is oxidized by the oxygen ions and releases electrons to an external circuit, thereby producing electricity which drives an electric motor that powers the automobile. The electrons then travel to the cathode, where they release oxygen from air, thus continuing the electricity-generating cycle. Individual fuel cells can be stacked together in series to generate increasingly larger quantities of electricity.
While a promising alternative in automotive technology, fuel cells are characterized by a low operating temperature which presents a significant design challenge. Maintaining the fuel cell stack within the temperature ranges that are required for optimum fuel cell operation depends on a highly-efficient cooling system which is suitable for the purpose.
Cooling systems for both the conventional internal combustion engine and the fuel cell system typically utilize a pump or pumps to circulate a coolant liquid through a network that is disposed in sufficient proximity to the system components to enable thermal exchange between the network and the components. Such cooling systems are usually subject to imposed coolant pressure limits which are based on component or system durability concerns. Because of various factors such as system design constraints and coolant temperature, many of these cooling systems exhibit significant variations or fluctuations in system resistance to coolant flow during the course of normal system operation. Thus, these systems are particularly vulnerable to producing coolant pressures which exceed the coolant pressure limits for the systems. The fuel cell cooling system has been found to manifest a particularly wide variation in coolant pressures over the normal operating range of the system.
Without the use of controls to reduce coolant pressure in a cooling system as needed for maintaining the coolant pressure within the imposed coolant pressure limits, the durability and operational integrity of the system or of system components may be compromised, requiring inordinately frequent system maintenance, repair and/or replacement. Because coolant systems for both fuel cell systems and conventional internal combustion engines lack a mechanism for measuring and controlling coolant system pressures, there is an established need for a method which is effective in controlling the pressures of coolant in a cooling system to prevent coolant pressures from exceeding pressure limitations for the system.